1. Field of the Invention
The invention relates to heat transfer interfaces such as gaskets that provide a path for heat transfer between two surfaces.
2. Description of Related Art
Much of thermal management involves the transfer of heat from one element, such as electronic components, boards and boxes, heatpipes, radiators, heat spreaders, etc. to another. Of major concern in this process is the thermal contact resistance of the interface between the two components. While individual components might have very high conductance, large temperature drops (ΔT's) can develop at high resistance interfaces, limiting overall performance of the thermal control system. The entire thermal management system can be greatly improved by using thermal interfaces with lower resistance. Smaller ΔT's can result in weight reduction, better performance, and longer lifetimes of electronic elements (e.g. batteries).
Existing methods of thermal attachment include bonding (brazing, soldering, adhesives, tapes) or bolting/clamping, often with a filler such as a thermal gasket or grease. The ideal interface will fill the gaps between the two elements with high thermal conductivity material. It will be compliant so that only a minimal amount of pressure is required for intimate contact, precluding the need for heavy bolts or clamping mechanism, and eliminating the necessity of flat, smooth mating surfaces. Furthermore, it will not fail under stresses induced by thermal expansion mismatch.
Conventional thermal gaskets consist of small, roughly spherical particles (e.g. alumina, BN, Ag) suspended in a compliant polymeric media such as silicone. Although each particle has high thermal conductivity, the interface between the particles has low conductance. The effective κ of the composite is limited by these numerous interfaces and the highest κ achieved is of the order of only a few W/mK.
As an alternative to the above described thermal interface material such as thermal greases, arrays of substantially parallel carbon fibers has been used. Some example systems of this type are provided by U.S. Pat. Nos. 5,077,637 to Martorana et al., 5,224,030 and 5,316,080 to Banks et al., and 4,849,858 and 4,867,235 to Grapes et al. The disclosures of each of these five patents are hereby incorporated by reference herein in their entireties.
Although carbon fiber based gaskets have increased thermal conductance over many other alternatives, their promise has not been realized, and further improvements to the efficiency of heat transfer for these types of gaskets is needed.